How do I combine two queries (union all) into one row?

Question

I have a tricky situation in trying to get information from multiple queries into a single row.

Consider the following table:

CpuUage:
    Time    ti         


        

Answer 1

This is a pivot table query. (Search on that if you require further info.)

The query structure you want is something along the lines of the following:

SELECT  groupname,
        SUM(CASE WHEN subsys = 'NORM' THEN jobs ELSE 0 END) AS NormJobs,
        SUM(CASE WHEN subsys = 'NORM' THEN cpu ELSE 0 END) AS NormCpu,
        SUM(CASE WHEN subsys = 'SYS7' THEN jobs ELSE 0 END) AS Sys7Jobs,
        SUM(CASE WHEN subsys = 'SYS7' THEN cpu ELSE 0 END) AS Sys7Cpu,
        SUM(CASE WHEN subsys NOT IN ('NORM', 'SYS7') THEN jobs ELSE 0 END) AS OtherJobs,
        SUM(CASE WHEN subsys NOT IN ('NORM', 'SYS7') THEN cpu ELSE 0 END) AS OtherCpu
FROM    ???
GROUP BY groupname

Answer 2

It's a typical pivot query - here's how you'd do it with CASE statements:

  SELECT t.group,
         SUM(CASE 
           WHEN t.subsys = 'NORM' THEN t.jobs 
           ELSE NULL
         END CASE) AS NormJobs,
         SUM(CASE 
           WHEN t.subsys = 'NORM' THEN t.cpu
           ELSE NULL
         END CASE) AS NormCpu,
         SUM(CASE 
           WHEN t.subsys = 'SYS7' THEN t.jobs 
           ELSE NULL
         END CASE) AS Sys7Jobs,
         SUM(CASE 
           WHEN t.subsys = 'SYS7' THEN t.cpu
           ELSE NULL
         END CASE) AS Sys7Cpu
    FROM CPUUSAGE t
GROUP BY t.group

Unfortunately, DB2's CASE statements need to end with END CASE, when Oracle/SQL Server/MySQL/Postgres doesn't. Well, PLSQL supports END CASE...

There's also the PIVOT syntax, which is also supported on Oracle 11g, and SQL Server 2005+.

Answer 3

I don't understand the problem with sub-querying, it seems like it should be just as fast:

select
    sub.gn as groupname,
    sum(sub.nj) as NormJobs, sum(sun.nc) as NormCpu,
    sum(sub.sj) as Sys7Jobs, sum(sub.sc) as Sys7Cpu
  from (
      select
          groupname as gn,
          sum(jobs) as nj, sum(cpu) as nc,
          0 as sj, 0 as sc
        from tbl
          where subsys = 'NORM'
          group by groupname
        union all select
            groupname as gn,
            0 as nj, 0 as nc,
            sum(jobs) as sj, sum(cpu) as sc
          from tbl
          where subsys = 'SYS7'
          group by groupname
    ) as sub
    group by sub.gn
    order by 1